Gear pump



F. E. NORLIN Aug. 5, 1958 -GEAR PUMP Filed Jan. l2. 1955 or" rarac'als.fjyoflzlm fnv@ United States Patent GEAR PUMP Francis E. Norlin,Chesterland, Ohio, assignor to Borg- Wamer Corporation, Chicago, Ill., acorporation of Illinois Application January 12, 1955, Serial No. 481,305

Claims. (Cl. 103-11) This invention relates to hydraulic power units,and is particularly concerned with an improvement in an arrangement ofiixed displacement intermeshing gear type pressure generators or pumpswherein the pumps of such an arrangement operate to delivernon-compressible liquid pressure to a resistance consumer or motor andwherein automatic means function to vary the output of one of said pumpsover a range of pressures according to the demand for pressure made uponthe arrangement by said motor.

In the U. S. Patent 2,505,191 there was disclosed an effective andcommercially practical arrangement for effective unloading a selectedone of a group of pressure generators upon the occurrence of apre-determined maximum delivery pressure without unloading the entireoutput of the generators by means of complicated and expensive valvestructures. In that patent, the liquid pressure generating unitcomprising a pair of intermeshing gear pumps of the pressure loaded typehaving at least one set of axially adjustable pressure loadable endplates or bearing bushing dening means (sometimes hereinafter referredto as bushings) was disclosed as disposed in a unitary housing with thepressure loadable bushings of each of the separate pumps responsive toloading pressure generated by their respective gears which loadingpressure is effective under pre-determined conditions to maintain saidbushings in pumping seal engagement with the corresponding side faces ofthe pump gears. The unit was further characterized by the incorporationin said housing of a pilot control or unloading valve means responsiveto the combined or joint output pressure of said pumps. When thecombined pressure reached a selected maximum value, the pilot controlvalve functioned to relieve the loading pressure acting on the bushingsof one of the pumps thus permitting the relieved bushings to moveaxially out of sealing engagement with the adjacent gear side facespermitting the pressure generated by said one of the pumps to return toinlet. In this unit the unloaded condition of the selected pump wasmaintained until a pre-determined minimum pressure condition was reachedwhereby the selected pump was again loaded.

The above described unit, as shown in the Lauck patent, was particularlycharacterized by being operable to provide a well-defined and clear-cutpressure point at which a selected one of the pumps was to be unloadedand maintained unloaded without the presence of hunting or cutting in orout of said selected pump which usually means that the selected pump tobe loaded or unloaded delivers usually either full ow or zero ilowduring its operation.

However, it has been found in practice that it is particularly desirableto have the pump selected to load and unload under pre-determinedconditions to deliver not only full ow and zero ow as the selected pumpwould do when constructed in accordance with the teachings of theaforementioned Lauck patent but, to deliver rice a partial rate of ilowaccording to the` demand made upon the unit by the resistance consumermotor. This partial rate of flow demand made upon the selected pump inthe arrangement described in the Lauck patent 2,505,- 191 caused what isknown as chattering caused by the inter-cooperation andinter-relationship in effective sizes of the unloading valve and theaxial movable bushings. For example, it has been found that in order forthe selected pump to supply a partial rate of flow after having beenunloaded it is necessary that its bushings travel from a fully unloadedposition to some intermediate position between the pumping seal positionwhen the pump is fully loaded and the fully unloaded position. Underthese circumstances the bushings, being sensitive to the pressuredemand, over-travel or go beyond the desired intermediate position andmust return to the desired intermediate positioncausing hunting orchattering. Ob-

viously, too, the action of the bushings of the selected pump candetrimentally offset the operation of the unloading valve.

It is, therefore, a primary object of my invention to improve thearrangement described in the Lauck patent by providing that arrangementwith a means to allow the pump, selected to unload and load, to delivernot only full flow or zero flow of fluid but also partial flow of iluidaccording to the demand made on the entire unit without chattering orover-travel on the part of the bushings of the selected pump.

Briefly, my invention incorporates in the arrangement of the type hereindescribed a shuttle type device which effectively cooperates with theunloading valve and thev pressure loadable bushings in the pump selectedto deliver a range of ilow which will temporarily stop the.y

bushings immediately prior to reaching their partial llow position fromthe fully unloaded position and then allow the bushings to travel totheir selected intermediate posi-A tion after a short interval of time.This momentary stopping of the bushings in their travel and thenallowing them to proceed to their iinal position acts to decreaseover-travel thus minimizing chattering, allowing the power unit todeliver any ow rate the consumer motor may demand. It has been foundalso that the shuttle device tends to dampen out pulsations or surges inthe outlet or discharge during the partial ow of the operation of thepower unit by transferring these pulsations and surges to the pressureloading chamber where they can escape through the unloading valve toinlet pressure. A more complete operation of my present in vention willbe explained in detail hereinafter. l

Accordingly, it is a specific object of my invention to to allow saidpower unit to deliver, without chattering,`

any iiow rate the system or consumer motor may demand.

A still more specific object of my invention is to incorporate a shuttletype device in a power unit of they type herein described which willreduce pulsations and surges in the discharge side of the power unit.

Other and more particular objects, advantages and usesof my inventionwill become apparent from vthe reading of the following specificationtaken in accordance with the appended drawings forming a part thereofand where- A Figure 1 is a schematic, partially sectional view of a`hydraulic pressure power unit constructed in accordance with my presentinvention showing to advantage the construction and arrangement of theanti-chattering shuttlev device; and

Figure 2 is an enlarged size, schematic in partially sectional view of apressure control chamber and a portion of the bushing and housing shownin Figure 1.

Referring in greater detail `to the embodiment shown in the drawings,there is shown a liquid pressure power unit, indicated in its entiretyas 10, comprising a unitary housing 11 having a common low pressureliquid inlet 12, a common high pressure outlet 13 and incorporatingtherein a first intermeshing gear type pressure generator or pressureloaded pump P-1, a second intermeshing gear type pressure generator orpressure loaded pump P-2, a one-way check valve assembly V, a pilotcontrol or unloading valve assembly C and a shuttle control deviceassembly S.

Pressure loaded pump or liquid pressure generator P-1 is preferablyconstructed in general conformity with the disclosure and claims of theU. S. Patent 2,420,622 to Roth et al. and comprises essentially a pairof intermeshing gears (one shown) indicated in their entirety as 17mounted on axially extending shafts (drive shaft 18 being shown)received in a pump chamber 19 formed in the housing 11 and journalled ina pair of xed body bushings 20 (one shown) and a pair of axiallymovable, pressure loadable, bearing bushing defining means 21 (oneshown) engaging the gear side faces on one side thereof in pumping sealrelation. The bushings are formed radially co-extensive with the gearteeth and sufcient clearance is provided between the axially movablebushings 20 and the adjacent end wall 21 of the housing to permit axialmovement of the bushings.

In the operation of a pump of the pressure loaded type, a portion of thedischarge pressure generated by the intermeshing gears is communicatedfrom the outlet or discharge side thereof to annular motive pressuresurface areas 22 at the back of the axially movable bushings. Thebushings including motive surface areas 22 cooperate with the adjacentwall 21 of the housing to define behind each bushing an annular pressureloading or motive pressure chamber indicated in its entirety as 23.Escape of pressure rearwardly of the pressure loading chambers 23 issubstantially prevented by means of an O-ring seal 24 disposed about therear portion of each bushing in a suitable annular groove formed in theperiphery of the bushing or in the adjacent bore wall. Any pressureleaking past the O-ring seals 24 may be vented to inlet pressure or to azone of intermediate pressure in accordance with conventional pressureloaded pump practice as set forth in the above-referred-to Roth et al.Patent 2,420,622 or in the Lauck Patent 2,505,191.

To provide an initial sealing relationship between the bearing bushingdefining means and the gear side faces coiled compression springs 25 aredisposed against the bushings to urge the forward surfaces thereof intoengagement with the gear side faces.

In the usual pressure loaded pump constructed in accordance with theteachings of the aforementioned Roth et al. Patent 2,420,622, reliefrecesses, such as 26, are formed in each of the radially inner portionsof the forward or gear engaging surfaces of the axially movable pressureloadable bushings 20 and are placed in communication. with a pressurelower than the discharge pressure generated by the pump'through aclearance between the gear journals and the bushing bores or by specificgrooves or channels 28 extending axially of the inner cylindricalsurface of the bore of the bushings. These recesses 26 control theeffective pressure area relationship between the rear or motive surfaces22 and the forward gear engaging surfaces of the pressure loadablebushings, the area and size of these recesses being determined iny anyparticular pump so as to control the effective pressure in such a mannerthat the axial force resulting from the pressure generated by the pumpacting against the forward gear engaging surfaces of the bushingstending to produce an axial movement of the bushings away from the gearside faces is effectively controlled and overcome by the oppositelydirected loading forces acting against the rear or motive surfaces 22 ofthe bushings which latter axial forces are made, in practice, toslightly exceed the first mentioned axial forces and thereby maintainsealing engagement with the gear side faces.

The secondary pump P-2 is constructed in a manner identical to that ofpump P-l, hence no detailed description thereof is deemed necessary. Itwill be noted that in the arrangement described in the aforesaid patentt0 Lauck 2,505,191, the small displacement pump P-2 is disclosed ashaving a different construction of its bushings and its housing in orderto provide the maximum motive surface area on the back face of thebushings, the particular construction of which was disclosed and claimedin Wichorek Patent 2,472,031. However, in view of the schematic showingof this application, the pressure loadable bushings of pump P-2 areshown as having a construction identical to that of the pressureloadable bushings 20 of the pump P-1.

One-Way check valve assembly V between pump P-l and pump P-2 comprises adisc-like valve proper 30 seating in the direction of flow from pump P-lwith coiled compression spring 32 functioning to urge the valve proper30 in the direction of its seal. Delivery of pressure from the pump P-1is effective to open valve 30 and permit ilow from pump P-1 to thecommon outlet 13 while any tendency of liquid to flow from pump P-2 inthe direction of discharge side of pump P-l is prevented by theautomatic closing of the valve proper 30.

Pilot control valve assembly C comprises disc-like or conically shapedvalve proper 33 suitably chambered for axial movement in housing 11 andurged in the direction of its seat by means of coil compression spring34 against the flow of fluid from the combined discharge pressure ofpumps P-l and P-2 when pump P-1 is discharging full or partial flow oragainst the output pressure of pump P-2 when pump P-l is fully unloaded;this pressure communication being effective through passage 35. Reducedstem 36 connects the valve proper 33 with motive piston 37, motivesurface 38 of which is responsive to the discharge of pumps P-1 and P-2,as aforesaid, through passage 35. O-ring seal 39 is disposed in suitablyformed grooves in piston 37 to prevent pressure communication leakingpast motive surface 38 toward valve proper 33. Valve proper 33 is inpressure communication with motive pressure chambers 23 of pump P-1through passage 40 and it is important to note that the area 41 ofpiston 37 facing valve proper 33 is the same as the effective area ofvalve proper 33 thus completely balancing valve proper 33 against anyinfluence exerted by pressure from passage 40. In other words, thedevelopment of pressure acting upon the motive surface area 22 in motivechambers 23, while in communication through passage 40 with valve proper33, nevertheless has no influence on valve proper 33. Thus valve proper33 is completely and entirely responsive to the delivery of pressureupon check valve assembly V which is the delivered pressure of bothpumps P-1 and P-2 when pump P-1 is fully or partially loaded and thedelivered pressure of pump P-Z when pump P-l has been fully unloaded.Too, pump P-Z, while of small displacement, is of sufficient capacity tomake up for any losses by leaks, etc. and at the same time maintain therequisite pressure or motive surface 38 of piston 37 for the purpose ofmaintaining valve proper 33 open until the llow demand becomes more thanpump P-2 can deliver. Obviously, spring 34 can be adjusted in anysuitable manner for the purpose of varying its compression value.Opening of valve proper 33 communicates pressure in line 40 from motivepressure chamber 23 to inlet 12 by means of passage 43.

Shuttle type device S comprises an enlarged piston portion 45 and areduced piston portion 46 suitably chambered for axial movement inhousing 11. Enlarged V piston portion 45 has a motive surface area 47subject t pressure in chambers 23 acting upon the motive pressureresponsive surfaces 22 through passages 40 and 48. Chamber 49 formed bythe housing 11, reduced piston portion 46 and area 50 on the sideopposite motive surface area 47 is vented to inlet pressure throughpassages 51 and 43. Motive pressure surface 53 on reduced stem portion46 at the other extremity of shuttle device S from motive pressure area47 is communicated to outlet 13 passage so as to be responsive to thecombined discharge pressure .of pumps P-1 and P-2, or to the dischargepressure of pump P-Z when pump P-l is fully unloaded through passageway54 and restricted orifice 55 formed to communicate with outlet passage13. It is important to note also that discharge pressure delivered bypump P-1 intermediate the discharge side of gears 17 and one-way valveassembly V to pressure loading chambers 23 and to motive surface area 47of shuttle device S will be restricted in its ow by orifice 56 formed,in the embodiment shown, in the housing. The purpose of restrictedorifices 55 and 56 will be explained fully hereinafter.

In the operation of a hydraulic power unit of the type herein described,upon the starting of pump P-1 and P-2, by rotation of common drive shaft18, pressure in common high pressure outlet 13 will rise, determined, ofcourse, by the relative displacements of pumps P-1 and P-Z and thepressure demand of motor M-l. The combined pressure in outlet 13, uponreaching the predetermined pressure level, acts upon motive surface area38 of piston 37 in unloading valve C to open valve proper 33 andrelieved of fluid pressure in motive chambers 23 acting upon the rear ormotive surfaces 22 of the axially movable bushings of pump P-1 thuspermitting the bushings 20 to move axially away from or out of pumpingseal engagement with the side faces of gears 17. This action unloadspump P-1 as hereinbefore described, and unless the iiow demand made uponthe unit is more than the ow that can be developed by the relativelysmall displacement pump P-2, the bushings 20 of pump P-l will come torest against the pump housing-the fully unloaded position of bushings20. It can be seen that at any flow demand on the unit between a fullow, developed by both pumps P-1 and P-2 fully loaded, and the iiowdeveloped by the small pump P-2, when P-1 is fully unloaded, will movethe bushings 20 to positions intermediate the position of pumping sealengagement and the fully unloaded position such as some intermediateposition in the partial flow range indicated in Figure 2.

A study of Figure 2 will show that the movement of the bushings 20 in atypical operation of a unit of the type herein described that anyintermediate position of partial flow development is at a very smalldistance from the gear side face. The distances actually involved in atypical unit is between iive thousandths of an inch from the gear sidefaces'. The remainder of the distance that the bushings travel, from thepumping seal engagement position adjacent the gear side face to thefully unloaded position against the pump housing, is for the purpose ofrelieving any back pressure developed inside the pump P-l and by-passingthis back pressure to inlet across the gear side faces. Obviously, anyinternal or back pressure in pump P-1, under these circumstances, isvery small.

During operation, as the flow demand on the unit is such that the iiowdeveloped by the pump P-2 is sufcient, pump P-2 will maintain unloadingvalve C open and bushings 20 will be in their fully unloaded positionwith no further delivery of pressure from pump P-1 past one-way checkvalve assembly V. Obviously, under these conditions, shuttle device S isin an upward (as viewed in Figure l) position by action of the pressurein passage 54 acting on motive surface area 53; the pressure acting onmotive surface area 47 having been "6 relieved to inlet. Orifice 55between discharge outlet 13 and passage 54 is employed for the purposeof slowing shuttle device S in its upward travel.

When the motor M-1 demands more flow than pump P-2 can deliver, thepressure developed by pump P-2 drops and unloading valve C tends toclose because of this drop of pressure acting on motive surface area 38and by action of `spring 34 in opposition thereto. This movement ofunloading valve C, creates an oriice, formed by valve proper 33 and itscorresponding seat, which is set slightly less in size than orifice 56adjacent vthe pumping gears 17 of pump P-1. As soon as the orifice inunloading valve C is created, pressure in the pressure loading chamber23 begins to rise to equal any back pressure in pump P-l intermediatethe discharge side of gears 17 and one-way valve assembly V.

When the pressure in pressure loading chamber 23 rises suiiiciently toequal any back pressure in pump 'P-l, pressure loading of the bushings20 begins and the bushings are urged toward the gear side faces of gears17. As the bushings move toward the gear side faces, and approach thepartial flow range, as more clearly indicated in Figure 2, pressure inpump P-l concurrently begins to rise and pressure in the pressureloading chamber also increases since the pressure developed by P-l iscommunicated to the pressure loading chamber 23 through orifice 56. Thisconcurrent pressure increase continues until the internal or backpressure in the pump P-l slightly exceeds the pressure developed by thepump P-2, at which time one-way valve assembly V opens and pump P-lstarts delivering flow to the common discharge outlet 13.

In order to reduce over-travel and hunting of the bush-` I ings andreduce chattering of the unit during the action of the bushingsdescribed in the above paragraph which occurs when partial ow isdemanded of the unit, shuttle type device S has been arranged to have aneffective pressure area relationship with respect to the bushings 20such that immediately prior to the pressure in pump P-l reaching thevalue suflicient to open one-way check valve -assembly V and deliver owinto the common discharge outlet 13, the pressure rise in conduits 40and 48 will act upon motive surface area 47 of piston 45 to start thepiston on its downward (as viewed in Figure l) stroke. While piston 45is travelling downwardly, the bushings 20 stop their movement toward thepumping gear side faces by reason of the fact that any iiow throughvorifice 56 is now used to move the piston 45 instead of the bushings 20.As soon as the piston 45 reaches the end of its stroke, the bushings 20again resume their travel toward the gear side face, however, thebushings have only a little distance to travel.

Turning again now to Figure 2 it can Ibe seen that the distance that thebushings travel to reach their partial ow position is relatively longand because lof this the bushings have a tendency to over-travel andhunt with resultant chattering of the pump. Now with the unbalance ofthe effective pressure area of the shuttle device p with respect to thebushings 20 as aforesaid, the bushings will 4cease their travelimmediately prior to their reaching their partial -iiow position, suchstopping point being either at the beginning of or slightly within thepartial flow range, until the shuttle device piston has completed itsfull stroke. When shuttle device piston reaches the end of its stroke,the bushings will resume their travel to their desired position.

ln a typical example of the length of travel of the bushings it has beenfound that from fully unloaded position to the beginning of the partialflow range, is a distance of approximately fifty thousandths of an inchwhile the remaining distance that the bushings travel after the shuttledevice comp'letse its stroke can vary f 7 the full fifty-one tofifty-five thousandths without pause.

It is important to note also that when the axially movable bushings 20are in any of their partial flow positions in the 4partial dow rangeindicated in Figure 2 they are susceptible to -movement by anyfluctuations or surges in the high pressure output line 13. A surgetoward higher pressure is normally expected to urge the bushings awayfrom the gear side faces because of the increase in pressure acrossforward gear engaging surfaces of the bushings, however, it can be seenthat any such surges will also urge shuttle device S toward its upwardposition. This movement, of course, tends to increase the pressure inconduits 49 and 48 by the action of motive surface 47 which istransferred to chamber 23. Thus the axially movable bushings, normallyexpected to move further away from the gear side faces, will remainsubstantially immovable in their desired position. In other words, theshuttle device S tends to dampen out pulsations and surges that may takeplace in the outlet line 13 by transferring them to the pressure loadingchamber.

Wherein the various parts of my invention have been referred to as beinglocated at 4the right or left or in an upward or downward position itwill be understood that this was done solely for the purpose offacilitating description and that such references relate only to therelan tive positions of the parts as shown in the accompanying drawing.

While my present invention has been disclosed in connection with certainspecific embodiments it is to be understood that these are to be by wayof example rather than 'limitation and that my invention is defined bythe appended claims which should be given a scope consistent with theprior art.

I claim:

1. In a liquid pressure generating power unit, means defining anenclosing housing having a first pump chamber receiving a first pair ofintermeshing gears, endplate bushing and bearing defining means normallyreceived in pumping seal engagement with the side faces of said gears,said bushings each including a terminal surface radially outwardlycoextensive with the adjacent gear teeth and engaging with the adjacentgear side face in pumping seal relation, said bushing means including apressure responsive surface opposed to said terminal surface and spacedfrom the adjacent housing wall forming with said housing a motivepressure chamber, means delivering liquid pressure generated by thecorresponding gears to said pressure chamber for normally urging saidbushing means into pumping seal engagement with the corresponding gearside face; a second pump chamber in said .housing receiving a secondpair of interrneshing gears, said housing having a common inlet to saidpairs of gears and a common outlet therefrom, a one-way check valve insaid housing interposed between said pairs of gears effective to preventreverse flow from said second pair of gears to said first pair of gears;means defining passage means interconnecting said pressure chamber withsaid inlet whereby the fluid in said pressure chamber is adapted to passto said inlet; means defining a control valve assembly disposed in saidpassage means effective upon the occurrence of a combined dischargepressure of a selected value to relieve said pressure uid from saidpressure chamber and permit said bushing means to move axially out ofsealing Contact with the associated gears to a position which eitherfully or partially unloads said first pair of gears by controlling theamount of fluid passing through said passage means, while said secondpair of gears continues to deliver liquid pressure to said commonoutlet; and means in fluid communication with said passage meansintermediate said pressure chamber and lsaid control valve assemblyeffective to reduce the overall movement of said bushing means from afully loaded or fully unloaded position to any partially loadedposition.

2. In a liquid pressure generating power unit, means delining anenclosing housing having a first pump chamber receiving a first pair ofintermeshing gears, end plate bushing and bearing seal defining meansnormally received in pumping seal engagement with the side faces of saidgears, said lbushings each including a terminal surface radiallyoutwardly coextensive Vwith the adjacent gear teeth and engaging withthe adjacent gear side face in pumping seal relation, said bushing meansincluding `a pressure responsive surface opposed to said terminalsurface and spaced from the adjacent housing wall forming with saidhousing a motive pressure chamber, means delivering liquid pressuregenerated by the corresponding gears to said pressure chamber fornormally urging said bushing means into pumping seal engagement with thecorresponding gear side face; a second pump chamber in said housingreceiving a second pair of intermeshing gears; said housing having acommon inlet to said pairs of gears and a common outlet therefrom, aone-way check valve in said housing interposed between said pairs ofgears effective to prevent reverse flow from said second pair of gearsto said first pair of gears; means defining passage meansinterconnecting said pressure chamber with said inlet whereby the fluidin said pressure chamber is adapted to pass to said inlet means defininga control valve assemblyl disposed in said passage means effective uponthe occurrence of a combined discharge pressure of a selected value torelieve said pressure uid from said pressure chamber and permit saidbushing means to move axially out of sealing contact with the associatedgears to a position which either fully or partially unloads said firstpair of gears by controlling the amount of fiuid passing through saidpassage means, while said second pair of gears continue to deliverliquid pressure to said common outlet; and means in fluid communicationwith said passage means intermediate said pressure chamber and saidcontrol valve assembly effective to reduce the overall movement of saidbushing means from a fully loaded or unloaded position to any partiallyloaded position as the ow demand on the power unit varies and isreflected in the liquid pressure level in said common outlet and actingon said control valve assembly.

3. In a liquid pressure generating power unit, means dening an enclosinghousing having a rst pump chamber receiving a first pair of intermeshinggears, end plate bushing and bearing defining means normally received inpumping seal engagement with the side faces of said gears, said bushingseach including a terminal surface radially outwardly coextensive withthe adjacent gear teeth and engaging with the adjacent gear side face inpumping seal relation, said bushing means including a pressureresponsive surface opposed to said terminal surface and spaced from theadjacent housing wall forming with said housing a motive pressurechamber, means delivering liquid pressure generated by the correspondinggears to said pressure chamber for normally urging said bushing meansinto pumping seal engagement with the corresponding gear side face; asecond pump chamber in said housing receiving a second pair ofintermeshing gears, said housing having a common inlet to said pairs ofgears and a common outlet therefrom, a one-way check valve in saidhousing interposed between said pairs of gears effective to preventreverse iiow from said second pair of gears to said first pair of gears;means defining a control valve assembly effective upon the occurrence ofa combined discharge pressure of a selected value to relieve saidpressure fluid from said pressure chamber and permit said bushing meansto move axially out of sealing contact with the associated gears to aposition which either fully or partially unloads rst pair of gears, saidcontrol valve assembly including means defining a pressure responsivemotive surface and a'pair of pressure balanced surfaces, means sealingsaid pair of balanced surfaces from communication with said first valvemotive surface, means placing said valve motive surface in communicationwith the combined output pressure of said two pairs of gears beyond saidcheck valve, means defining passage means placing said pressure in saidpressure chamber in communication with said balanced surfaces of saidvalve, whereby said pilot valve is moved to open position in response toa selected value of combined output pressure acting on said valve motivesurface or to a closed position in response to the combined outputpressure falling below the selected pressure value and is for relievingor increasing the pressure in said pressure chamber uninfiuencedby thepressure liquid acting in said pressure chamber; and means in fluidcommunication with said passage means intermediate said pressure chamberand said control valve assembly effective to reduce the overall movementof said bushing means from a fully loaded or unloaded position to anypartially loaded position as the flow demand on the power unit variesand is reflected in the liquid pressure level in said common outlet andacting on said control valve assembly.

4. In a high pressure noncompressible liquid power generating unitcomprising means defining a housing having a low pressure liquid inlet,a high pressure liquid outlet and a pair of pump chambers therein; meansdefining a first pair of fixed displacement intermeshing gear units in afirst one of said chambers; means defining a second pair of relativelysmall fixed displacement intermeshing gears in a second one of saidchambers, end plate bearing and pumping seal defining means adjacent oneside face of said gears in each of said chambers, each of said end platemeans having a first surface radially outwardly coextensive with theadjacent gear teeth and engageable with the gear side face in bearingand pumping seal relation, said end plate means having a second opposedsurface responsive to liquid pressure generated by the correspondinggears effective to hold said end plate means in pumping seal relationwith the corresponding gear side faces; a one-way check valve in saidhousing interposed between the outlet side of the gear teeth of saidfirst pump and the outlet side of the gear teeth of said second pump forpreventing reverse fiow from said second pump to said rst pump; meansconnecting said pumps in continuous driving relation; control valvemeans in communicationy with the pressure acting on the rear surface ofthe bushing means of one of said gear units for relieving said loadingpressure, said control valve including a pressure responsive motivesurface and means placing said motive surface of said control valve incommunication with the joint output pressures of said two pumps wherebythe occurrence of an output pressure of a selected predetermined valuebecomes effective to operate said control valve relieving the loadingpressure on said first-named pump and permitting the corresponding endplate means to move out of pumping seal engagement with the gear sidefaces to a position which either fully or partially unloads said firstpump, said second pump continuing to deliver liquid pressure to saidoutlet; and means defining a shuttle device in pressure communicationwith said control valve, common outlet and loading pressurecommunication means effective 'to reduce the overall movement of-saidend plate means from a fully loaded or unloaded to any partially loadedposition.

5. In a high pressure liquid power generating unit comprising meansdefining a housing having a low pressure liquid inlet, a high pressureliquid outlet and a pair of separate pump chambers therein; a first pairof fixed displacement intermeshing gears in a first one of saidchambers; a second pair of relatively small fixed displacementintermeshing gears in the second one of said chambers, means connectingsaid pairs of gears in continuous driving relation, an end plate in saidfirst pump chamber having a backface normally spaced from the adjacentend wall of said corresponding pumpl chamber and having portionscooperable with said housing to provide a pressure chamber, said endplate also having afront terminal face subject to the pressures incommunication with the corresponding gear teeth and cooperable with theadjacent position I i side face' of the' corresponding gear to normallyprovide a pumping seal therewith, a relief recess formed in the gearengaging face of said end plate radially inwardly of its outerlperiphery to limit the effective sealing area between said end plateand said gear side face, a spring interposed between said housing andthe outer terminal of said end plate effective to assure an initialpumping seal upon starting, means establishing communication 'betweensaid relief recess and said inlet, means establishing restricted fiowcommunication between the discharge side of the corresponding gears andsaid pressure chamber at the back face of said end plate, the relationof the area of said back face to said sealing area being such that theforce acting upon said back face `of said end plate normally slightlyexceeds the force acting on said front face whereby to maintain saidpumping seal without excessive friction wear or loss in volumetricefiiciency; control valve means in communcation with the pressure actingin said pressure chamber for relieving the same to permit said end plateto move axially out of pumping seal engagement with the associated gearside face toa position which fully or partially unloads said gear, saidcontrol valve'including means defining a pressure responsive motivesurface, means placing said motive surface of said control valve incommunication with the combined output pressures of said two pumpswhereby the generation of a combined output pressure of a selectedpredetermined value becomes effective to operate said control valverelieving the loading pressure in said chamber,V thus fully or partiallyunloading or fully or partially re' -loading said first pair of gears,said second pump continuing to deliver liquid pressure to said outlet;and means defining a shuttle device in pressure communication with saidcontrol valve, said outlet and pressure chamber effective to reduce theoverall movement of said end plate means from a fully loaded or unloadedposition to any partially loaded position.

V6. In a liquid pressure, power generating unit, means defining a firstintermeshing gear type pump; means defining a second relatively smallcapacity intermeshing gear type pump; means connecting said pumps incontinuousl driving relation; said pumps having a common inlet `anddelivering to a common outlet; one-way check valve means interposedbetween the discharge sides of the gears of said pump effective topermit flow from said first pump' to said second pump but preventingflow from said second pump to said first pump; said first pump includingan axially adjustable end plate engageable with the associated gear sideface for providing a pumping seal therewith and means for deliveringpressure fiuid generatedby the corresponding gears into communicationwith the rear surface of said end plate for pressure loading said endplate; and means defining a control valve assembly effective upon thegeneration of a common outlet pressure of predetermined selected valueeffective to relieve the loading pressure from communication with therear surface of said end plate and thus fully or partially unload saidfirst pump, said control valve assembly including va valve proper incommunication with the pressure acting on said rear surface of said endplate, spring means normally urging said valve in the direction of itsseat against the flow from said back face, motive means connected withsaid valve effective when operated to open or close said valve andrelieve or increase said loading pressure, means placing said motivemeans in communication with the combined output pressure from said pumpsbeyond said check valve, said valve and motive means including opposedbalanced surfaces rendering said valve assembly nonresponsive to thepressure acting on the back face of said end plate; and means defining ashuttle device in pressure communication with said loading pressure,valve assembly and combined output pressure effective to assist saidfirst pump in reaching a partially unloaded condition from a fullyloaded or unloaded condition.

7. In a liquid pressure generating power unit, means defining anenclosing housing containing a rst intermeshing gear pump and a secondintermeshing gear pump, said housing having a common inlet to said pumpsand a common outlet therefrom, saidpumps having means connecting thesame in continuous driving relation, each of said pumps includingaxially adjustable end plates, defining pumping seals with the adjacentgear side faces, means placing the rear surfaces of said plates incommunication with pressures generated by the respective pumps effectiveto pressure load said plates, a one-way check valve in said housingeffective to permit flow from said rst pump to said common outlet butpreventing ow from said second pump to said first pump, means defining acontrol valve assembly including a valve proper in pressurecommunication with the rear surface of the end plate of said first pumpand seating against the ow therefrom, coil compression spring meanshaving a selected compression value effective to urge said valve in tledirection of its seat with a predetermined force, motive piston meansconnected with said valve for moving the same away from said seat, meansplacing said motive piston in pressure communication with the combineddischarge pressures from said first and second pumps beyond said checkvalve, whereby the generation of a combined output pressure of aselected maximum value becomes effective to move said control valve toopen position and relieve the loading pressure from the back face of theend plate of said first pump, While said second pump continues todeliver pressure uid to said common outlet; and means defining a shuttledevice in pressure communication with said rear surface, control valveand combined output pressure effective to assist said first pump inreaching a partially loaded condition from a fully loaded condition whensaid loading pressure is relieved and in reaching a partially loadedcondition when said loaded pressure is increased by said control valvemoving toward closed position.

8. In a high pressure liquid power generating unit comprising a housinghaving a low pressure liquid inlet, a high pressure liquid outlet, meansdefining a first relatively large displacement intermeshing gear typepump in said housing, means defining a second relatively smalldisplacement intermeshing gear type pump in said housing, meansconnecting said pumps in continuous driving relationship, each of saidpumps comprising axially adjustable end plates, means directing thedischarge pressure from the respective pumps to the back faces of saidend plates for pressure loading the same; means defining a control valvearrangement in pressure communication with the backface of the end plateof the relatively large displacement pump, said control valve having amotive piston means placing said motive piston in communication with thecombined outlet pressures of said rst and second pumps effective uponthe occurrence of a combined output pressure of a selected predeterminedvalue to operate said valve and relieve the loading pressure from theback side of said end plate associated with said relatively largedisplacement pump, said second relatively small displacement pump beingeffective to continue delivering pressure fluid to said common outlet;and means defining a shuttle device in pressure communication with saidrear surface, control valve and combined output pressure eiective toassist said first pump in reaching a partially loaded con- 12 ditionfrom .a fully loaded condition when said loading pressure is relievedand in reaching a partially loaded condition when said loaded pressureis increased by said control Valve moving toward closed position.

9. In a liquid pressure power generating unit, means defining a firstintermeshing gear type pump of the type employing pressure loadedbushings, means defining a second intermeshing gear type pump, a commoninlet and a common outlet for said pumps, means interposed between theoutlet sides of said first and second pumps effective to prevent flowfrom the second pump to the first pump, means defining pressure controlchamber means in said first pump, said chamber means being adapted toreceive liquid pressure to effect loading of said bushings, means deningpassage means interconnecting said chamber means with said inlet, saidpassage means being adapted to permit the passage of liquid from saidchamber means to said inlet, valve means disposed in said passage meansresponsive to the generation of a combined delivery pressure of apredetermined value effective to cause full or partial unloading andfull or partial reloading of the pressure loaded bushings of said firstpump by controlling the amount of liquid passing from said chamber meansto said inlet while maintaining said second pump in operation, and meansin fluid communication with said passage means intermediate said chambermeans and said valve means effective to assist said first pump inreaching a partially loaded condition from a fully unloaded conditionwithout chattering.

10. A hydraulic power unit including a first intermeshing gear typepump, pressure loadable bushings associated with the gears of said pump,said bushings being movable axially away from the associated gears to aposition which fully or partially unloads said pump, a secondintermeshing gear type pump, a common inlet and a common outlet for saidtwo pumps, means defining pressure control chamber means in said rstpump, said chamber means being adapted to receive liquid pressure toeffect loading of said bushings, means defining passage meansinterconnecting said chamber means with said inlet, said passage meansbeing adapted to permit the passage of liquid from said chamber means tosaid inlet, valve means disposed in said passage means responsive to thegeneration of a combined delivery pressure of a predetermined valueeffective to cause unloading of the first pump by controlling the amountof liquid passing from said chamber means to said inlet whilemaintaining said second pump in operation to deliver liquid pressure,and means in fluid communication with said passage means intermediatesaid chamber means and said valve means effective to assist saidbushings in reaching any partial loading position from a fully loaded orunloaded position with a minimum of overtravel.

References Cited in the file of this patent UNITED STATES PATENTS2,440,371 Holley, Ir Apr. 27, 1948 2,505,191 Lauck Apr. 25, 19502,512,025 Lauck June 20, 1950 2,589,067 Erickson Mar. l1, 1952 2,617,361Neal Nov. ll, 1952 2,617,477 Isreeli Nov. ll, 1952

